In recent years, there is a demand for easy measurement of colors without using dedicated measurement apparatuses such as an expensive spectrophotometer and a colorimeter. As for the demand, recent digital cameras have been becoming more reasonable, are capable of obtaining the colors of a target object as gray levels (hereinafter referred to as “color value”) in the R (red) G (green) B (blue) color space, and may thus be used for color measurement at a low cost.
However, the color tone of an image photographed by the digital camera often differs from the original color tone due to the influence of light such as illumination light or sunlight under the photographing environment. Thus, it is difficult to stably perform color measurement.
Accordingly, in a case where the color tone of the photographed image differs from the original color tone, color correction may be performed in which the colors of pixels in the image are converted into the original colors.
In a common method for performing color correction, known colors (hereinafter referred to as “reference color”) are simultaneously photographed with the target object, and true colors of pixels of an input image are obtained by using color changes of the reference colors.
In general, all pixel values of the input image may not be provided beforehand as the reference colors. Thus, conversion amounts of input colors are calculated from plural reference colors, and the color correction is thereby performed. That is, the colors of input pixels are corrected by performing interpolation in the color space.
As related art about such a kind of color correction, a technology has been suggested in which control signals of an output device for the input signals in the input color space are obtained by interpolation between preset vertex output values of respective color separation components that are set to the vertices in the input color space which are divided into plural solid figures. In this technology, the reference colors are set such that finer division is performed for areas in the color space that are important in expression and for the color spaces with high frequencies in order to reduce non-linear errors that occur in volume interpolation and linear interpolation.
Japanese Laid-open Patent Publication No. 10-70669 is an example of related art.